Electrically operated primer



INVENTOR WILLIAM E. SHEEHA/V ATTORNEYS FIG. 2

Dec. 7, 1954 w. E. SHEEHAN ELECTRICALLY OPERATED PRIMER Filed Oct. 1'7,1951 Unite States Patent ELEoTRrcALLY OPERATED PRIMER William E.Sheeh'an, Silver Spring, Md.

Application October 17, 1951, Serial No. 251,806 1 Claim. or. 102- 865(Granted under Title 35, U. s. code 1952 mazes This invention relates toexplosive priming devices, and more particularly to an improvedelectrically ac tivated igniter for initiating the explosion of largercharges of explosives.

Primers of the above character usually comprise a closed cup adapted tobe secured in an explosive device adjacent the main explosive orpropellant charge and contain a highly sensitive ignition compositionand a flash charge. The ignition composition may be gun cotton or othersensitive compositions known in the art and is usually formed about asingle high resistance filament known as a bridge wire, which isconnected in the electrical firing circuit. The arrangement is such thatas the bridge wire is heated upon closing of the firing circuit thesensitive composition ignites and develops sufficient heat to set offthe flash charge which in turn fires the main explosive or propellantcharge of the device with which the primer is used.

Prior art primers of the above character make use of a lead-in wire toconnect a bridge wire to an external source of electricity and as suchare subjetc to scaling problems about the lead-in wire or wires whichmay result in the entrance of moisture into the ignition compound, thusincreasing the probability of misfires or adversely affecting thepredetermined time delay, before teh main or propellant charge is fired.Another disadvantage in such devices resides in the possibility of oneor both of the lead-in wires being broken thereby preventing theestablishment of an electrical circuit at the desired time to fire theignition charge. It will also be apparent that the single loop bridgewire which is usually made of flimsy material may be broken during roughhandling, thus further increasing the percentages of misfires or duds.Since the bridge wire is inaccessible for inspection such a defect willgo unnoticed until an attempt is made to fire the explosive charge.

Although the number of misfires encountered in a series of explosioinsmay be relatively small, each misfire constitutes a potential source ofserious injury or possible death to the individual whose task it is toremedy the fault. The removal of the explosive material is extremelydangerous especially in blasting operations because the explosivematerial may be difficult to locate in some instances and may blow upaccidentally due to various causes while searcihing for it. In ordnanceequipment a misfire will reduce the fire power of the weapon used or incases of automatic weapons the weapon itself may be jammed, thussubjecting those whose lives are dependent upon the operation of suchweapons to imminent danger.

The present invention avoids the disadvantages of prior art devices ofthis character by providing a single electrode which forms an electricalcircuit through a plurality of bridge wires and then to ground throughthe surface of the primer and also permits the use of a plurality ofbridge wires which are readily aflixed within the igniter cup so as toprevent misfires due to poor electrical contact within the igniteritself.

With the foregoing in mind it is an object of the present invention toprovide an igniter which affords unform firing results by theestablishment of mamixurn contact between the initiating composition andthe electrical bridge wires which serve to ignite the composition.

Another object is the provision of a preassernbled hermetically sealedigniter element for use in detonator primers which is positive inaction, rugged in construction, compact in design, and economical tomanufacture.

Still another object is to provide an igniter element which lends itselfto quantity production.

Yet another object is the provision of an igniter bridge assembly whichmay readily be varied in size to provide for different ignitionrequirements.

These and other objects, and their attendant advantages will become moreapparent from the following description when read in conjunction wdiththe accompanying drawings in which:

Fig. 1 is a longitudinal sectional view of an electrically actuatedprimer illustrating an embodiment of the present invention;

Fig. 2 is a sectional exploded view of a portion of Fig. 1 showing thedetailed arrangement of parts that make up the electrical primer of thepresent invention; and

Fig. 3 is a perspective view of the igniter bridge assembly.

Referring now to the drawings wherein like numerals designate the sameparts throughout the several views and more particularly to Fig. 1wherein there is disclosed a casing 10 which is externally threaded forattachment to a projectile or any other great charge of explosive andinternally threaded to receive a locking sleeve 11 which is adapted tohold a preassernbled electrical ignition element or primer designatedgenerally by the numeral 50, firmly in place in a cavity formed in thecasing 10. The electrical ignition element comprises a flanged electrode12 the neck portion of which extends through an opening in the base 13of the casing it and is insulated fromthe edges of the opening by anannular insulating sleeve or bushing 14. The electrode 17. is made ofbrass or any suitable electrically conductive material and is formedwith an enlarged head portion 15 which is mounted within a metallicprimer cup 16 and insulated therefrom by an apertured insulating disc 17and a sleeve 18 composed of fiber, plastic, or any other insulatingmaterial and the neck portion of the flanged electrode 12 extendsthrough the cup 16 and through an opening in the base of the casing 10.The primer cup 16 serves to hold the elements of the primer in positionand also to provide a ground connection through the casing 10.

In juxtaposition and in electrical contact with said enlarged headportion 15 and insulated from the cup 16 is a bridge assembly shown inFig. 3 which comprises a pair of annular laminae or washers 19 and 20made of electrically conductive material such as copper, axiallyseparated by and bonded to an insulating ring 21 made of laminatedphenolics, or other suitable insulating .material. Connecting thewashers or laminae 19 and 20 are one or a plurality of looped bridgewires 22 made of a high resistant material such as platinum iridiumalloy, nichrome tungsten or other similar materials which wires areattached to the inner periphery of said washers by soldering, brazing,staking or other suitable means. The looped portions of bridge wires 22extend longitudinally through a chamber or cavity 23 formed by theassembled washers 1Q and 2th and ring 21. The chamber or cavity 23 isfilled with a nonconductive igniter composition 24 such as gun cotton ordiazodinitro phenol surrounding and in intimate contact with the loopedportions of wires 22 which serve as igniters for the composition. An analternative the chamber 23 may be filled with a conductive ignitercomposition such as lead styphnate-graphite which will eliminate the useof the bridge wires 22. The chamber 23 is sealed on the left by theflange 15 of the electrode 12 and on the right by a relatively thinmetallic disc 25 of electrically conductive material. Seated against thedisc 25 is an ignition spacer sleeve 26 formed of brass or otherconductive material and having an annular opening therein which carriesa flash charge 27 of black powder or other suitable material to be setoff by the igniter composition 24. The flash charge chamber is closed atthe right end by a second metallic disc 28. The disc 28 is in electricalcontact with an inturned flange portion 29 of primer cup or housing 16which is formed by crimping or other similar means so as to complete anelectrical circuit from a source (not shown) through electrode 12,washer 19,

a bridge wire or wires 22, washer 20, disc 25, sleeve 26, disc 28,primer cup 16, and thence to the grounded casing 10.

The primer element 50 is assembled separately from casing andhermetically sealed by coating an annular space 30 with Bakelite or anyother suitable sealing compound and adding a fillet of the same materialat the junction of flange 29 and disc 28.

The assembled primer element 50 is inserted in casing 10 and held inposition by locking sleeve 11 as disclosed above. Booster charge 31 isadded in a chamber of the locking sleeve 11 and the chamber closed offby an exteriorly threaded cylinder 32 having apertures 33 in the wallsthereof which permit the flash of booster charge 31 to reach apropellant charge (not shown). The assembled casing 10 and primerelement 50 are thenplaced in contact with a large charge of explosivesor inserted in an ordnance sleeve and ignited by closing any well knownfiring circuit. The closing of the circuit causes current to flowthrough the elements as described above which, due to the highresistance of bridge wires 22, produces sufiicient heat in the wires toignite the com position 24. The ignition of composition 24 will burnthrough disc 25 to explode flash compound 27 which in turn burns throughdisc 28 to explode the booster charge 31 thereby setting oi the largecharge of explosives.

While the device disclosed herein is a preferred embodiment of theinvention it is to be understood that the invention may be embodied inother forms without departing from the spirit or scope of the inventionas defined by the appended claim.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

An electrically operated primer for firing a propellant chargecomprising; a metallic cup, an electrode having an enlarged head portionmounted partially within said cup and insulated therefrom and a neckportion extending beyond said cup for connection to a source ofelectricity, an electrically conductive annular lamina in juxtapositionand in electrical contact with said electrode and insulated from saidcup, a second conductive annular lamina spaced axially from the firstlamina and insulated from said cup, an insulating ring disposed betweensaid conductive laminae, said laminae and said ring forming a cavity, afirst igniting composition charge in said cavity, a plurality of highresistance loop bridge wires spaced from each other on the innerperiphery of said laminae for igniting said first charge electrically,the ends of said wires being connected to said laminae and a portion ofsaid wires extending longitudinally through said cavity in contact withsaid first charge, a first conductive disc in electrical contact withthe second lamina and enclosing one end of the cavity, an electricallyconductive ignition spacer sleeve seated against the first disc andhaving an annular opening therein, a second flash composition chargewithin said annular opening, said first disc and the sleeve beinginsulated from the cup, a second destructible conductive disc inelectrical contact with the spacer sleeve and the cup for enclosing theannular opening containing the second charge, and means on said cup inelectrical engagement with the second disc, said means restraining axialmovement of the component parts to maintain operative engagement.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 520,116 Mason May 22, 1894 676,219 Bryant et a1 June 11, 19011,084,745 Lindsay Jan. 20, 1914 1,313,801 Doran Aug. 19, 1919 2,142,583Yarbrough Jan. 3, 1939 FOREIGN PATENTS Number Country Date 4,449 GreatBritain of 1910

